This was simple physics: the larger form factor could fit a larger 2,500 mAh battery, while that year's iPhone 4s had a ~1430 mAh battery, and the Galaxy S2 from a few months earlier had a 1,650 mAh battery. I strongly suspect battery life was the main reason large phones eventually became mainstream, as phones could continue increasing performance without sacrificing all-day (or even two-day) battery life. Samsung continued releasing new Galaxy Note phones on a regular basis, and slowly but surely, larger phones became mainstream.